1. Field of the Invention
The present invention relates to a power generation apparatus based on a Rankine cycle employed in a binary power generator and the like.
2. Description of the Related Art
In terms of energy conservation, recent years have seen an increased need for electric power generators that collect so-called “waste heat” from various types of facilities such as factories and generate electricity using the energy from the collected waste heat. Because the “waste heat” does not have, in many cases, a sufficiently high temperature to allow generation of water vapor that drives steam turbines used for general electric power generators, there has been a demand for electric power generators capable of generating electric power by means of low temperature heat.
As such an electric power generator, a binary power generator constituting a Rankine cycle heat engine has been known, for example, as described in JP S60-144594 and described by Naoyuki INOUE and five others in “Development of a Power Generation Unit Driven by Waste Heat (Study on Working Fluids and Expansion Turbines)”, Ebara Engineering Review No. 211, p. 11-20, April 2006, EBARA CORPORATION. The binary power generator comprises an evaporator for evaporating a low boiling point working medium, an expander such as a turbine for causing expansion work of the working medium vapor to drive an electric generator, a condenser for condensing the working medium vapor, and a circulating pump for pressurizing the working medium to resupply the evaporator with the pressurized working medium, which are connected in series to form a closed loop for circulating the working medium.
In the Rankine cycle heat engine, an amount of energy that can be extracted by the expander matches, in theory, is a difference between an enthalpy of the working medium at an outlet of the evaporator and an enthalpy of the working medium at an inlet of the condenser. In an ideal condition, the working medium is caused in the expander to undergo isentropic change through which the pressure of the working medium is reduced to a condensing pressure in the condenser.
For a cold source for cooling the working medium in the condenser, an inexpensive medium such as coolant water produced through a cooling tower is typically used. This causes a condensing temperature in the condenser, i.e. the condensing pressure of the working medium to vary with the seasons. That is, in conventional power generation apparatuses, the temperature of the coolant water becomes higher in summer, which in turn increases the temperature and pressure, i.e. the enthalpy of the working medium at the inlet of the condenser. Thus, there has been a problem in that, due to the increased enthalpy, an amount of energy that can be extracted by the expander (i.e. a power generation capacity in a case where the expander is used for driving the electric generator) is decreased.